This proposal seeks continuation funding for the Integrated Health Interview Series (IHIS), the nation's most comprehensive source for data and metadata describing the health of the U.S. population. The continuation will expand and enrich IHIS by adding the Household Component of the Medical Expenditure Panel Survey (MEPS), the most complete source of information on population healthcare use and expenditures. This initiative comes at a critical time. The U.S. healthcare system is undergoing unprecedented changes in response to the Affordable Care Act. New efforts promise to transform the healthcare system away from a clinical acute care model to a population-based focus on improved health. The IHIS data system will allow scientists and policy researchers to easily access the data needed to study change and to make informed decisions. Over the past ten years, the IHIS project has successfully harmonized 50 years of NHIS data, including 5.5 million person records and over 12,000 variables describing the health and health behaviors of the U.S. population, and made these data freely available via a user-friendly web application. Adding MEPS data to IHIS and updating the web access system will greatly multiply the power of this critical piece of health data infrastructure. The content of MEPS is complimentary to that of the NHIS; MEPS collects detailed information on individual healthcare use and costs, allowing researchers to estimate average U.S. per capita healthcare spending and study expenditures by medical condition and type of healthcare service. The MEPS data are longitudinal and linkable to the NHIS; a subsample of households responding to the previous year's NHIS is selected to participate in the MEPS and is interviewed five times over a two-year period. The expanded IHIS database will add 22 years of health expenditure microdata (1996-2018), providing longitudinal data on health and healthcare for approximately 520,000 NHIS respondents, and 5 years of NHIS microdata (2014-2019). This continuation project will develop new access tools to capitalize on the longitudinal dimension of the MEPS, build linkages across the two surveys, and create more than 2,000 integrated variables. Accomplishing this goal will require restructuring the MEPS data into a consistent format, creating comprehensive machine- readable documentation of each MEPS file, and developing harmonized metadata describing the relationship between files. The expanded and upgraded IHIS will provide an invaluable on-line data resource that will reduce barriers to research on the health of the U.S. population and the use and costs of healthcare services at a critical point in the history of American healthcare.